Method of making an electromagnetic transducer



Nov. 4, 1969 T w. 1. GIRDNER 3,475,815

METHOD OF- MAKING AN ELECTROMAGNETIC TRANSDUCER Original Filed June 14,1965 2 Sheets-Sheet 1 F lgure 3 (c) INVENTOR WILLIAM I. GIRDNER BY WQWMATTORNEY I Figure 3(b) Nov. 4, 1969 w. GIRDNER 3,475,815

METHOD OF MAKING AN ELECTROMAGNETIC TRANSDUCER Original Filed June 14,1965 2 Sheets-Sheet 2 W26 g l 40 20? V II 0'34 J12 l A n igure 4 (a) Figure 4(b) INVENTOR WILLIAM I. GIRDNER ATTORNEY United States Patent3,475,815 METHOD OF MAKING AN ELECTROMAGNETIC TRANSDUCER William I.Girdner, Portola Valley, Califi, assignor to Hewlett-Packard Company,Palo Alto, Calif., a corporation of California Original application June14, 1965, Ser. No. 463,496, now Patent No. 3,404,242, dated Oct. 1,1968. Divided and this application May 13, 1968, Ser. No. 728,435 Int.Cl. H011? 7/06; Gllb /42 US. Cl. 29-603 11 Claims ABSTRACT OF THEDISCLOSURE A generally-spool-shaped member is formed from a body ofnonmagnetic material. Circular shoulders are formed around the centralportion of this spool-shaped member. A pair of matching bracket-shapedside frames are then formed from portions of the spool-shaped member onopposite sides of a plane containing its longitudinal axis. Thesematching side frames are joined together to provide a pair of spaced,oppositely facing, convexly arcuate inner surfaces having pairs ofspaced, oppositely facing, transversely aligned shoulders. Anelectromagnetic transducer is fixedly engaged between each of thesepairs of shoulders, and a shielding element is fixedly positioned oneach side of each transducer between the oppositely facing, convexlyarcuate inner surfaces of the side frames.

CROSS-REFERENCE TO RELATED APPLICATION This is a divisional applicationof patent application, Ser. No. 463,496 entitled Magnetic Element andMethod for Making the Same and filed June 14, 1965 by William I.Girdner.

BACKGROUND AND SUMMARY OF THE INVENTION This invention relates tomagnetic transducer heads and methods for making the same.

The principal object of this invention is to provide an improvedmagnetic transducer head and an inexpensive method for making the same.

Other and incidental objects of this invention will become apparent froma reading of this specification and an inspection of the accompanyingdrawing in which:

FIGURE 1 shows the side frame of a magnetic transducer head of the priorart;

FIGURE 2 shows the side frame of a magnetic transducer head inaccordance with this invention;

FIGURE 3 shows the method of making a magnetic transducer head inaccordance with this invention; and

FIGURE 4 shows a completed magnetic transducer head made'in accordancewith the method of FIGURE 3.

Referring to FIGURE 1, there is shown the side frame of a conventionalmagnetic transducer head comprising two generally bracket-shapedmatching halves and 12 which are fastened together face-to face. Eachhalf is made of a nonmagnetic material such as aluminum. The flatvertical inner surface of each half is interrupted by a plurality ofrectilinear shoulders 14 for supporting the magnetic elements (notshown) of the transducer head. It is important that the distance 16between opposite shoulders 14 be as large as possible at the contactsurface 18 of the side frame. This distance 16 is limited by therequirement of a small side frame that is structurally rigid. For eachhalf the shoulder pattern must be held to very close tolerancesdimensionally'and should be, insofar as possible, the mirror image ofthe shoulder pattern of the other half. Typically, the shoulders 14 areformed individually by a precision milling operation which is verycostly.

3,475,815 Patented Nov. 4, 1969 CC p DESCRIPTION OF THE PREFERREDEMBODIMENT Referring now to FIGURE 2, there is shown the side frame of amagnetic transducer head according to one embodiment of this inventioncomprising two generally bracket-shaped matching halves 10 and 12 ofnonmagnetic material. These halves 10 and 12 have oppositely slopingfront surfaces rounded to an appropriate radius at the apex thereof toprovide the side frame with a generally convex contact surface 18. Eachhalf has an arcuate vertical inner surface interrupted by a plurality ofarcuate shoulders 14. The arcuate vertical inner surface of each halfmakes it possible to increase the distance 16 between opposite arcuateshoulders 14 at the contact surface 18 of the side frame without loss ofstructural rigidity because of the increased nonmagnetic materialtowards the center of each half. The shoulders 14 may be provided with afiat surface or with lips 20 as shown in the drawing to more rigidlysupport the magnetic elements of the transducer head. In either case theshoulder pattern of each half is formed by a method described below soas to be dimensionally stable and precise and substantially the mirrorimage of the shoulder pattern of the other half.

According to this invention, the magnetic transducer head may be made bythe method indicated in FIGURE 3. In making the side frame a shaft ofthe desired nonmagnetic material is rigidly mounted for rotation aboutits longitudinal axis and is cut during such rotation to form thespool-shaped member shown in the elevational view of FIGURE 3(a). Theplurality of circular shoulders 14 each having a pair of circular lips20 is also formed during rotation of the shaft, for example, with amulti-element cutter adjusted to give the desired shoulder pattern. Thisoperation may be simply performed with the required precision by aconventional screw machine. The spoolshaped member is next cut in halfand machined to form the appropriately shaped halves 10 and 12 of theside frame as indicated in FIGURE 3( b) which is a top view of thespool-shaped member of FIGURE 3(a).

This method of making the side frame for the magnetic transducer head ismore simple and substantially less expensive than the conventionalmethod of precision milling the individual shoulders for each half ofthe side frame. Moreover, the reduction in cost is obtained without anysacrifice in dimensional precision, identity of the matched halves, andstructural rigidity. In fact, there may be significant improvement inthe first two of these features due to the concentricity maintainedduring simultaneous formation of the two halves and in the last featuredue to the arcuate vertical inner surface of each half.

The transducer head is completed by rigidly positioning anelectromagnetic element 22 between the lips 20 of each shoulder 14 ofthe matching halves of the side frame as indicated in FIGURE 3(0). Thesematching assemblies are then lapped to provide each with a smooth matingface 24. The lapped pole tip 26 of each electromagnetic element is nextcoated with a nonmagnetic material, and the matching assemblies arejoined together at the mating faces 24 thereof. Shielding elements 36and 40' (shown in FIGURE 4) are then firmly positioned on either side ofeach electromagnetic element 22. Finally, the contact surface 18 of thecompleted magnetic transducer head is provided with a smooth finish.

Referring to FIGURES 4(a) and (b) there is shown a front elevationalview and a sectional view respectively of a completed magnetictransducer head. Two matching electromagnetic elements 22 are firmlypositioned between the lips 20 of opposite shoulders of the matchinghalves 10 and 12. These electromagnetic elements 22 are generallyI-shaped and are made of a transformer iron core material. The pole tips26 of the matching electromagnetic elements define a narrow gap 28(shown greatly exaggerated in the drawing) which is filled with anonmagnetic material. If the magnetic transducer head is operated as arecording head, the input signals to be recorded are fed to one or morecoils 32 wound around the electromagnetic elements 22 as the recordmedium 30 is moved past this narrow gap 28. If it is operated as aplayback head, the movement of the record medium 30 past the gap 28causes output signals to be generated in the coils 32 wound on theelectromagnetic elements. Shielding plates 36 made of a mixture ofmagnetic and nonmagnetic materials are firmly positioned between theopposite surfaces 38 to prevent cross-talk between the signalsassociated with each electromagnetic element 22. Additional shieldingstrips 40 are firmly positioned at the contact surface 18 in the spacebetween the opposite lips 20. These shielding strips 40 and thecorresponding lips are made sufficiently thick to provide clearancebetween the coils 32 and the adjacent shielding plates 36 so as topermit the leads from the coils to be brought out the back side 42 ofthe magnetic transducer head.

I claim: 1. A method for making a transducer head, said methodcomprising the steps of:

forming a pair of matching, generally bracket-shaped side frame sectionseach having a convexly arcuate inner surface; joining these side framesections together in face-to-face relationship with their convexlyarcuate inner surfaces in spaced, oppositely facing, transversealignment; and mounting a transducer between the oppositely facing,convexly arcuate, inner surfaces of the side frame sections. 2. A methodas in claim 1 wherein said forming step comprises:

forming a generally spool-shaped body having a pair of generallycircular end portions and a generally circular intermediate portion ofsmaller diameter than the end portions; and forming the side framesections from portions of this spool-shaped body on opposite sides of aplane of symmetry containing the longitudinal axis of the spool-shapedbody, whereby the convexly arcuate inner surface of each side framesection comprises part of the periphery of the intermediate portion ofthe spool-shaped body. 3. A method as in claim 2 wherein said joiningstep comprises:

transposing the side frame sections with respect to the positions theyoccupied while part of the spoolshaped body; and joining the transposedside frame sections together at a plane of symmetry with their convexlyarcuate inner surfaces in spaced, oppositely facing, transversealignment. 4. A method as in claim 1 wherein: said forming step includesforming at least one convexly arcuate shoulder on the convexly arcuateinner surface of each side frame section; and said joining stepcomprises joining the side frame sections together at a plane ofsymmetry with their convexly arcuate shoulders in spaced, oppositelyfacing, transverse alignment. 5. A method as in claim 4 wherein saidforming step comprises:

forming a generally spool-shaped body having a pair of generallycircular end portions and a generally circular intermediate portion ofsmaller diameter than the end portions; forming at least one generallycircular shoulder on the periphery of the intermediate portion of thespoolshaped body; and

forming the side frame sections from portions of the spool-shaped bodyon opposite sides of a plane of symmetry containing the longitudinalaxis of the spool-shaped body, whereby the convexly arcuate '4 shoulderof each side frame section comprises part of the shoulder on theperiphery of the intermediate portion of the spool-shaped body. 6. Amethod as in claim 5 wherein: said forming step further comprisessevering the spoolshaped body along the plane of symmetry containing itslongitudinal axis and forming the side frame sections from the severedportions of the spool-shaped body; and said joining step comprisestransposing the side frame sections with respect to the positions theyoccupied while part of the spool-shaped body and joining the transposedside frame sections together with their convexly arcuate shoulders inspaced, oppositely facing, transverse alignment. 7. A method as in claim6 wherein: said mounting step comprises mounting a transducer element onthe convexly arcuate shoulder of each side frame section before saidjoining step; and including the additional step of lapping faces of theside frame sections and faces of the transducer elements to be mated ina plane of symmetry during the joining step. 8. A method as in claim 7wherein: said joining step further comprises joining the lapped faces ofthe side frame sections together at a plane of symmetry; and saidmounting step comprises joining the lapped faces of the transducerelements together between the spaced, oppositely facing, convexlyarcuate shoulders and in the same plane of symmetry as the lapped facesof the side frame sections. 9. A method as in claim 1 wherein: saidforming step includes forming a plurality of convexly arcuate shoulderson the convexly arcuate inner surface of each side frame section; andsaid joining step comprises joining the side frame sections together ata. plane of symmetry with their convexly arcuate shoulders in spaced,oppositely facing, transverse alignment. 10. A method as in claim 9wherein said forming step comprises:

forming a generally spool-shaped body having a pair of generallycircular end portions and a generally circular intermediate portion ofsmaller diameter than the end portions; forming a plurality of generallycircular shoulders on the periphery of the intermediate portion of thespool-shaped body; and forming the side frame sections from portions ofthe spool-shaped body on opposite sides of a plane of symmetrycontaining the longitudinal axis of the spool-shaped body, whereby theconvexly arcuate shoulders of each side frame section comprise parts ofthe shoulders on the periphery of the intermediate portion of thespool-shaped body.

11. A method as in claim 10 wherein said joining step comprises:

transposing the side frame sections with respect to the positions theyoccupied while part of the spoolshaped body; and joining the transposedside frame sections together with their convexly arcuate shoulders inspaced, oppositely facing, transverse alignment.

References Cited UNITED STATES PATENTS 2,888,522 5/1959 McCutchen et al.179-1002 3,349,193 10/1967 Vice 179-1002 JOHN F. CAMPBELL, PrimaryExaminer C. E. HALL, Assistant Examiner US. Cl. X.R. 29-463, 592

